I'm thinking Yasu is true, just that there is something else.Though I'm awaiting a pm to answer a question regarding Van Dine.

The problem is combining EP7 with any theory without Yasu as the sole culprit.

One thing seems pretty solid though. If anyone killed on that day outside of Yasu's orders, then that person must have hoped to make Yasu take the blame for their crimes. Whether they were planning any murders before Maria got that first letter or not, it's hard to imagine that they would miss this chance to blame these crimes on Yasu, especially after the FTs that always leave "Maria's Beatrice" as the most suspicious person.

__________________

"The only moral it is possible to draw from this story is that one should never throw the letter 'q' into a privet bush. But, unfortunately, there are times when it is unavoidable."
--Hitchhikers